In the manufacture of high reliability long life undersea cable, such as optical fiber telecommunications cable, the integrity of the high voltage insulation is an important factor limiting the life of the cable. One of the variables that affects the integrity of this insulation is surface defects, such as scratches created during manufacture. Increasingly, in both military and commercial applications, a requirement exists that even minute surface defects greater than, for example, 0.005 inches in depth be avoided.
Current techniques used by cable manufacturers to find surface defects on the insulation rely either upon visual inspection or human tactile feel. In the latter case, the inspector literally uses the sensitivity of the hand to detect surface defects.
The current inspection for surface defects thus is very costly because it entails unreeling and re-reeling the cable in a separate process step through an inspection station, at very slow speeds to allow for sufficient manual inspection time. The processes are also inherently inaccurate since they depend on the inspector's subjective interpretation of visual or tactile data. Experience has also shown that it is difficult for an inspector to maintain the necessary accuracy and concentraion during the manual inspection of long lengths of cable.